The present invention generally relates to robots for industrial use having an arm mechanism of a horizontal multiple articulated type.
Generally, robots called a horizontal multiple articulated type are used as robots for industrial use so as to automate an assembling operation and other operations.
FIGS. 7 and 8 show the construction principles of conventional robots of this type. FIG. 7 is a serial arm type robot as a first conventional robot. FIG. 8 is a parallelogram link arm type robot as a second conventional robot.
In FIG. 7(a), the serial arm type robot of the first conventional type includes a first prime mover 38, a second prime mover 39, arms 40, a grasping mechanism 41 to grasp an object 42 to be grasped, and a robot control unit 43. One end of a first arm 40a is mounted on the driving shaft of the first prime mover 38. The second prime mover 39 is disposed on the other end of the first arm 40a, and a second arm 40b is mounted on the driving shaft of the second prime mover 39. The grasping mechanism 41 is provided on the other end of the second arm 40b so as to grasp the object 42 ith the grasping mechanism 41. The first prime mover 38, the second prime mover 39 and the grasping mechanism are adapted to be controlled during action by the robot control apparatus 43.
The operation of the robot constructed as described hereinabove will be described hereinafter. The action instructions are given to the first prime mover 38, the second prime mover 39 and the grasping mechanism 41 from the robot control apparatus 43 in accordance with the operation data stored in advance within the memory (not shown) of the robot control apparatus 43 to cause the arms 40 to effect the desired actions so as to effect pick and place operations with respect to the object 42 to be grasped.
FIG. 7(b) shows the torques T1, T2 to be caused in the first prime mover 38 and the second prime mover 39 when the pick and place operations are effected. In FIG. 7(b), the revolution center of the first prime mover 38 conforms to the origin on the absolute coordinates axis (x-y), the angle formed by the first arm 40a and the y positive axis is .THETA.1, the angle to be formed by the second arm 40b and the first arm 40a is .THETA.2, the length of the first arm 40a, the mass, the inertial moment round the gravity center position, the force such as the frictional force to be caused in the bearing portion are respectively l1, m1, I1, F1, the length of the second arm 40b, the mass, the inertial moment round the gravity position, the force such as frictional force to be caused in the bearing portion are respectively l2, m2, I2, F2, the inertial moments of the first prime mover 38 and the second prime mover 39 are respectively Is1, Is2, the distance from the revolution center of the first prime mover 38 to the gravity center position (shown by the X mark in the drawing) of the second arm 40b is h2, the mass of the motor provided on the revolution central portion of the second prime mover 39 is considered a material point (shown by the .cndot. mark in the drawing) w1, the mass of the grasping mechanism 41 provided on the tip end portion of the second arm 40b is considered a material point (shown in the .cndot. mark in the drawing) w2. The production torque T1 of the first prime mover and the production torque T2 of the second prime mover are given by the following dynamic formula of Lagrange. ##EQU1##
As the coefficient (m2l1h2+w2l1l2) of the angle .THETA.2 formed by the first arm 40a and the second arm 40b cannot be made "0" in the respective formula, the size of the coefficient of the J11 is changed by a change in the .THETA.2. This shows the dynamic interference between the first prime mover 38 and the second prime mover 39 by the operation of the arm 40. A compensation control for avoiding the dynamic interference is necessary to be effected with respect to the first prime mover every time the second arm 40b operates, so that the control portion becomes composite and expensive.
The second conventional robot shown in FIG. 8 is provided in an effort to overcome the above described problem. In FIG. 8(a), the parallelogram link arm type robot provided as the second conventional robot includes a first prime mover 44, a second prime mover 45, arms 46, a grasping mechanism 47 to grasp an object 48 to be grasped, and a robot control apparatus 49. One end of the first arm 46a is mounted on the driving shaft of the first prime mover 44. Also, a second prime mover 45 is provided on the same shaft as the rotary shaft of the first prime mover 44, with one end of the second arm 46b being mounted on the driving shaft of the second prime mover 45. One end of a third arm 46c which is equal in length to the first arm 46a is coupled to the other end of the second arm 46b. A fourth arm 46d is coupled to the other end of the third arm 46c and to the other end of the first arm 46a so that the arm 46 constitutes the parallelogram link construction with four arms. A grasping mechanism 47 is provided on the other end of the fourth arm 46d so as to grasp the object 48 by the grasping mechanism 47. The first prime mover 44, the second prime mover 45 and the grasping mechanism 47 are adapted to be controlled in operation by the robot control unit 49.
The operation of the robot constructed as described hereinabove is the same as in the first embodiment, and the description thereof will be described.
FIG. 8(b) shows the torques T1, T2 to be caused in the first prime mover 44 and the second prime mover 45 when the robot effects a pick and place operation. In FIG. 8(b), the revolution center of the first and second prime movers conforms to the origin on the absolute coordinates axis (x-y), an angle to be formed with a first arm 46a and the y positive axis is .THETA.1, an angle to be formed by a second arm 46b and the x negative axis is .THETA.2, the length of the first arm 46a, the mass, the inertial moment round the gravity center, the force such as frictional force and to be caused on the bearing portion are respectively l1, m1, I1, F1, the length of the second arm 46b, the mass, the inertial moment round the gravity center, the force such as frictional force to be caused in the bearing portion are respectively l2, m2, I2, F2, the length of the third arm 46c, the mass, the inertial moment round the gravity center are respectively m3, I3 (the length is l1 as in the first arm 44), the length of the fourth arm 46d, the mass, the inertial moment round the gravity center are respectively (l2+l4), m4, I4, the inertial moments of the first and second prime movers are respectively Is1, Is2, the distance from the revolution center of the first prime mover 44 to the gravity center position (shown by the X mark in the drawing) of the first arm 46a from the revolution center of the first prime mover 44 and the distance to the gravity center position (shown by the X mark in the drawing) are respectively h1, h2, the distance from the tip end position of the second arm 46b to the gravity center position (shown by the X mark in the drawing) of the third arm 46c from the tip end position of the second arm 46b is h3, the distance from the tip end position of the first arm 46a to the gravity center position (shown by the X mark in the drawing) of the fourth arm 46d is h4, the mass of the grasping mechanism 47 which are provided in the tip end portion of the fourth arm 46d is considered the material point (shown by the .cndot. mark in the drawing) w1. The production torques T1 and T2 are given by the following dynamic formula of Lagrange. ##EQU2## where J11=m1h1.sup.2 +m3h3.sup.2 +m4l1.sup.2 +w1l1.sup.2 +I1+I3+Is1
J12=J21=(w4l1.sup.h 4-m3l2h3+w1l1h4).times.sin(.theta.1-.theta.2) PA1 J22=m2h2.sup.2 +m3l2.sup.2 +m4h4.sup.2 +w1l4.sup.2 +I2+I4+Is2 PA1 E11=E22=0 PA1 E12=-E21=-(m4l1h4-w3l2h3+w1l1hr)cos(.theta.1-.theta.2)
As .THETA.1 and .THETA.2 are included in respective formulas of J12, J21, E12 and E21, and the coefficients of .THETA.1 and .THETA.2 become (m4l1h4-w3l2h3+w1l1h4) in the (2) formula, dynamic interference is caused between the first and second prime movers during the operation of the arm 46 as in the first conventional embodiment if the coefficient is not "0". But a negative term is included in the coefficient (m4l1h4-m3l2h3+w1l1h4), so that it may be made "0" by devising a proper design of the arm. The terms J12, J21, Ell, E12, E21 and E22 all become "0" in the (2) formula, and J11 and J22 which do not include .THETA.1 and .THETA.2 have only constant values, with a large advantage that the robot may be operated comparatively stably with simple and inexpensive control apparatus without any dynamic interference between the first and second prime movers accompanied by the operation of the arm 46.
The parallelogram link arm type robot in the second conventional embodiment poses no problem when the robot arms alone are independently operated and the pick and place operation is effected with respect to an extremely light object. When an object as heavy as the mass of one arm or heavier than such mass is grasped, moved and placed, the arm tip end mass is changed greatly between the condition in which the weight is grasped and the condition in which the weight is not grasped. As the term w1 of the coefficient (m4l1h4-m3l2h3+w1l1h4) given in the description in the second conventional embodiment undergoes large changes, the above described coefficient which has been made "0" purposely in the condition where the object is not grasped is adapted to have a value other than "0" when the object has been grasped, thus causing the dynamic interference between the first prime mover of the robot and the second prime mover accompanied by the operation of the arm, which causes a serious problem in the stable operation of the robot.